Abstract： Objective To assess the filtration efficiency of two N95 filtering-facepiece respirators(FFRs)for the decomposition products of sulfur hexafluoride (SF6).Methods Two types of N95 FFRs (the particulate and the acid-proof respirators) were selected in this study.The decomposition products of SF6,including particles,hydrogen fluoride (HF) and sulfur dioxide (SO2),were measured under experimental condition by using TSI PortaCount Plus,fluorine ion-selective electrodes and spectrophotometer separately.The filtration efficiency was then calculated and compared.Results Both two models of N95 respirators had lowest filtration efficiency larger than 95％ for particles under airflow ranged from 10 to 95 L/min.When exposed to different concentrations of HF (low:0.00～ 1.99 mg/m3,middle:2.00～3.99 mg/m3,high:＞4 mg/m3),the acid-proof N95respirator was more effective than the particulate respirator (P＜0.05) with a filtration efficiency of 98.83％,99.08％,and 99.03％ versus 48.44％,45.71％,and 47.31％.For four SO2 concentration ranges (0.00～2.49 mg/m3,2.50～4.99 mg/m3,5.00-9.99 mg/m3,and ＞10.00 mg/m3),the acid-proof respirator showed a high filtration efficiency within exposure to 1.5 hours:95.73％,98.67％,98.14％,and 97.78％,respectively,when exposure duration extended to 4 hours,the filtration efficiency of the acid-proof respirator decreased to 91.97％,82.28％,70.12％,and 58.56％,respectively.Conclusion Both the particulate and the acid-proof N95 FFRs met national standards on the particulate filtration efficiency.The acid-proof N95 respirator demonstrates to be more effective in filtering HF and SO2 than the particulate respirator.The filtration efficiency could decrease to an unsafe condition under longer exposure duration,timely replacement of respirator is recommended at the workplace.